In cathode-ray tubes (CRTs) for image display used for television receivers, a horizontal deflection circuit and a vertical deflection circuit that respectively supply a horizontal deflection current and a vertical deflection current to a horizontal deflection coil and a vertical deflection coil are used, and electronic beams sent out of an electronic gun are deflected in the horizontal direction and the vertical direction by the operations of the circuits.
FIG. 21 is a circuit diagram showing an example of the configuration of a conventional horizontal deflection circuit. The conventional horizontal deflection circuit shown in FIG. 21 comprises a horizontal switching transistor (hereinafter referred to as a transistor) Q11, a resonant capacitor C11, a damper diode D11, a horizontal deflection coil L12, an S-correction capacitor C12, and a primary coil L11 of a deflection transformer.
One end of the primary coil L11 of the deflection transformer is connected to a power supply V11, and the other end thereof is connected to a node N11. The transistor Q11 has its collector connected to the node N11, its emitter connected to a ground, and its base to which a drive pulse DP which is synchronized with the horizontal frequency is applied.
The resonant capacitor C11 and the damper diode D11 are connected in parallel between the node N11 and a ground terminal. The horizontal deflection coil L12 and the S-correction capacitor C12 are connected in series between the node N11 and the ground terminal. The resonant capacitor C11, the damper diode D11, the horizontal deflection coil L12, and the S-correction capacitor C12 constitute a resonant circuit.
By the above-mentioned configuration, when the transistor Q11 is rendered conductive upon application of the drive pulse DP which is synchronized with the horizontal frequency to the transistor Q11, energy is supplied to the resonant circuit from the power supply V11 through the primary coil L11 of the deflection transformer. Accordingly, a deflection current having a predetermined slope flows through the horizontal deflection coil L12.
When the transistor Q11 is then rendered nonconductive, the resonant circuit resonates, whereby a resonant pulse voltage is generated by the energy previously stored. Consequently, a resonant pulse voltage is applied to the horizontal deflection coil L12 by the resonant circuit, so that a deflection current having a slope in the opposite direction to the predetermined slope flows through the horizontal deflection coil L12.
By repeating the above-mentioned operations, a sawtooth deflection current flows through the horizontal deflection coil L12. Consequently, a magnetic field is generated in the deflection coil L12, thereby making it possible to successively deflect electronic beams in the horizontal direction.
FIG. 22 is a block diagram showing another example of the configuration of the conventional horizontal deflection circuit. The conventional horizontal deflection circuit shown in FIG. 22 comprises a horizontal switching transistor (hereinafter abbreviated as a transistor) Q11, a power supply unit 101, a first resonant circuit 102, and a second resonant circuit 103.
The transistor Q11 has its collector connected to the power supply unit 101 and the first resonant circuit 102, its emitter connected to a ground, and its base to which a drive pulse DP which is synchronized with the horizontal frequency is applied. The first resonant circuit 102 comprises a horizontal deflection coil. The first resonant circuit 102 and the second resonant circuit 103 are connected in series. The first resonant circuit 102 is connected to the power supply unit 101, and the second resonant circuit 103 is grounded.
In the above-mentioned manner, resonance operations performed by the first and second resonant circuits 102 and 103 which are connected in series are controlled by the transistor Q11, so that a resonant pulse voltage is generated by the first and second resonant circuits 102 and 103 using energy supplied from the power supply unit 101.
FIG. 23 is a circuit diagram showing the configuration of the conventional horizontal deflection circuit shown in FIG. 22. The conventional horizontal deflection circuit shown in FIG. 23 comprises a transistor Q11, resonant capacitors C11 and C13, damper diodes D11 and D12, a horizontal deflection coil L12, a resonant coil L13, S-correction capacitors C12 and C14, and a primary coil L11 of a deflection transformer.
One end of the primary coil L11 of the deflection transformer is connected to a power supply V11, and the other end thereof is connected to a node N11. The power supply V11 and the primary coil L11 of the deflection transformer constitute the power supply unit 101 shown in FIG. 22. The transistor Q11 is the transistor Q11 shown in FIG. 22, and has its collector connected to the node N11.
The resonant capacitor C11 and the damper diode D11 are connected in parallel between the node N11 and a node N12. The horizontal deflection coil L12 and the S-correction capacitor C12 are connected in series between the node N11 and the node N12. The resonant capacitor C11, the damper diode D12, the horizontal deflection coil L12, and the S-correction capacitor C12 constitute the first resonant circuit 102 shown in FIG. 22.
The resonant capacitor C13 and the damper diode D12 are connected in parallel between the node N12 and a ground terminal. The resonant coil L13 and the S-correction capacitor C14 are connected in series between the node N12 and the ground terminal. The resonant capacitor C13, the damper diode D12, the resonant coil L13, and the S-correction capacitor C14 constitute the second resonant circuit 103 shown in FIG. 22.
By the above-mentioned configuration, a horizontal deflection circuit of a diode modulator type capable of correcting pincushion distortion and horizontal amplitude without varying a high voltage output generated by the deflection transformer is constructed.
FIG. 24 is a timing chart for explaining the operations of the horizontal deflection circuit shown in FIG. 23. As shown in FIG. 24, when the transistor Q11 is rendered conductive (an ON period T2 shown in FIG. 24) upon application of a drive pulse DP which is synchronized with the horizontal frequency to the transistor Q11, energy is supplied to the first and second resonant circuits 102 and 103 from the power supply V11 through the primary coil L11 of the deflection transformer, so that a deflection current IC having a predetermined slope flows through the deflection coil 13.
When the transistor Q11 is then rendered non-conductive (an OFF period T1 shown in FIG. 24), the first resonant circuit 102 and the second resonant circuit 103 respectively resonate, whereby resonant pulse voltages are respectively generated by the energy previously stored. Consequently, a resonant pulse voltage P is applied to the horizontal deflection coil L12 by the first resonant circuit 102 and the second resonant circuit 103, so that a deflection current IC having a slope in the opposite direction to the predetermined slope flows through the horizontal deflection coil L12.
By repeating the above-mentioned operations, a sawtooth deflection current IC as shown in FIG. 24 flows through the horizontal deflection coil L12. Consequently, a magnetic field is generated in the deflection coil L12, thereby making it possible to successively deflect electron beams in the horizontal direction.
In recent years, in the television receiver, the frequency is increased in a high-definition television, a monitor for a computer, and so forth, so that the horizontal frequency is liable to be increased. When the horizontal frequency is increased, the pulse width of the resonant pulse voltage P is narrowed. However, the amount of energy in the resonant pulse voltage P is determined by a power supply voltage. When the pulse width is narrowed, therefore, the pulse height is increased.
However, the pulse height of the resonant pulse voltage P is limited by the voltage resistance of the transistor Q11. Accordingly, the pulse height of the resonant pulse voltage P cannot be increased as it is. In order to obtain a predetermined deflection current, therefore, the inductance value of the horizontal deflection coil L12 must be decreased. When the inductance value is decreased, it is difficult to adjust a magnetic field generated by the horizontal deflection coil L12. Accordingly, the optical characteristics and the deflection distortion of the electron beams released form the cathode-ray tube are degraded.
Furthermore, the deflection current is inverse proportional to the inductance value of the horizontal deflection coil L12. When the inductance value of the horizontal deflection coil L12 is decreased, therefore, the deflection current is increased. Accordingly, the loss of power in each of electric devices through which the deflection current flows is increased, thereby increasing power consumption.